Black-Hole Spin Precession and its Astrophysical Implications

引力是自然界的四大基本力之一，爱因斯坦的广义相对论对其进行了描述。广义相对论最极端的预测之一是黑洞的存在，黑洞是一种密度很大的物体，其引力如此之大，以至于连光都无法逃脱。在如此极端的状态下研究引力，为更多地了解这一根本力量提供了最有希望的机会之一。广义相对论的另一个预测，即双星黑洞发出的引力波会拉伸和压缩时空，最近得到了美国国家科学基金会资助的激光干涉仪引力波天文台(LIGO)的证实。黑洞完全由它们的质量和自转来描述，但双星黑洞的自转通常与它们的轨道平面不对准，就像地球自转轴与其围绕太阳的轨道之间23度的不对准一样，这是季节的原因。广义相对论导致黑洞自转改变方向或进动；这种进动在LIGO观测到的引力波中留下了可检测到的信号。该奖项支持关于黑洞自旋进动以及它可以受到LIGO等引力波探测器限制的程度的研究。这项工作有助于科学家解释LIGO观测，从而更好地理解引力和黑洞的天体物理起源，这些黑洞是造成它们自转失调的原因。PI和合作者还将开发一种交互式虚拟现实模拟黑洞及其发出的引力波，该模拟将在网上免费提供，并通过德克萨斯大学达拉斯分校现有的推广网络在当地公共图书馆和博物馆展出。这些模拟帮助公众虚拟地体验引力波的影响，并提高公众的兴趣和对科学研究和教育的支持。这项提议的目标是提供一个全面的图景，说明双星黑洞自转与其轨道角动量之间的失调的起源和影响。人口合成代码将被用来探索初始自旋失调如何依赖于天体物理黑洞形成的各个方面，如质量转移、潮汐排列和超新星反冲。这些代码产生的自旋分布将从黑洞形成演化，直到它们开始发射可探测到的引力波，使用PI新开发的技术，在激发时间尺度上有效地计算自旋进动。一旦双星进入像LIGO这样的地面探测器的灵敏度带，LIGO算法库套件中的公开可用代码将被用于生成波形，并分析在现实的信噪比下，决定自旋进动的双星黑洞参数估计得有多好。PI和合作者还将执行和分析数值相对论模拟，以评估后牛顿预测在黑洞合并前最终轨道上自旋进动的可靠性。这项研究为天体物理模型的选择提供了基础，结合了许多事件对自旋失调的约束，以区分黑洞形成的天体物理模型，例如球状星团中的动力学形成(对于球状星团，自旋应该是各向同性的)和来自恒星双星的形成(应该显示出自旋排列的趋势)。最后的项目将考虑黑洞形成和合并之间的自旋进动如何影响对最终黑洞质量、自旋和引力反冲的预测。这个项目对LIGO观测到的恒星质量的黑洞和星系调查中寻找的从空间或运动学上偏离其宿主星系的反冲类星体都有影响。

Gravity is one of the four fundamental forces of nature and is described by Einstein's theory of general relativity. One of the most extreme predictions of general relativity is the existence of black holes, compact objects whose gravity is so intense that not even light can escape from them. Investigating gravity in such an extreme regime provides one of the most promising opportunities to learn more about this fundamental force. Another prediction of general relativity, that binary black holes emit gravitational waves that stretch and squeeze spacetime, was recently confirmed by the NSF-funded Laser Interferometer Gravitational-wave Observatory (LIGO). Black holes are fully described by their masses and spins, but the spins of binary black holes are generally misaligned with their orbital plane, much like the 23 degree misalignment between the Earth's rotation axis and its orbit about the Sun responsible for the seasons. General relativity causes black-hole spins to change direction or precess; this precession leaves detectable signatures in the gravitational waves observed by LIGO. This award supports studies on black-hole spin precession and the extent to which it can be constrained by gravitational-wave detectors like LIGO. This work helps scientists to interpret LIGO observations and thus better understand gravity and the astrophysical origin of black holes responsible for their spin misalignments. The PI and collaborators will also develop an interactive virtual-reality simulation of precessing black holes and the gravitational waves they emit which will be available free online and presented at local public libraries and museums through existing outreach networks of the University of Texas at Dallas. These simulations help the public virtually experience the effects of gravitational waves and enhance public interest and support for science research and education.This goal of this proposal is to provide a comprehensive picture of the origin and implications of misalignments between binary black-hole spins and their orbital angular momentum. Population-synthesis codes will be used to explore how initial spin misalignments depend on various aspects of astrophysical black-hole formation like mass transfer, tidal alignment, and supernova recoils. The spin distributions generated by these codes will be evolved from black-hole formation until they begin to emit detectable gravitational waves using the PI's newly developed technique for efficiently calculating spin precession on the inspiral timescale. Once the binaries enter the sensitivity band of ground-based detectors like LIGO, publicly available codes in the LIGO Algorithm Library Suite will be used to generate waveforms and analyze how well the binary black-hole parameters that determine spin precession can be estimated for realistic signal-to-noise ratios. The PI and collaborators will also perform and analyze numerical-relativity simulations to assess the reliability of post-Newtonian predictions for spin precession in the final orbits before black-hole merger. This research provides the basis for astrophysical model selection, combining constraints on spin misalignments from many events to distinguish astrophysical models of black-hole formation, such as dynamical formation in a globular cluster (for which spins should be isotropic) versus formation from stellar binaries (which should exhibit a tendency towards aligned spins). The final project will consider how spin precession between black hole formation and merger affects predictions for final black-hole masses, spins, and gravitational recoils. This project has implications both for the stellar-mass black holes observed by LIGO and recoiling quasars spatially or kinematically offset from their host galaxies sought in galaxy surveys.